Tokyo, Japan--Tokyo Institute of Technology (Tokyo Tech) researchers have synthesized approximately 1 nm sized blue-fluorescent molecular nanocapsules with an isolated cavity using green and inexpensive, eco-friendly zinc and copper ions. In sharp contrast to molecular capsules and cages composed of precious metal ions such as palladium and platinum that exhibit poor fluorescence, these photo-functional nanocapsules emit blue fluorescence with 80% efficiency and have potential applications in sensors, displays, biomedical imaging, and drug-delivery systems.1
Molecular cages and capsules can be prepared through a simple synthetic process called coordinative self-assembly. However, most of them are composed of precious metal ions such as palladium and platinum, and are non-emissive due to quenching by the heavy metals. Now, Michito Yoshizawa, Zhiou Li, and co-workers from the Chemical Resources Laboratory at Tokyo Tech Institute of Technology report novel molecular nanocapsules with the M2L4 composition (where M represents zinc, copper, platinum, palladium, nickel, cobalt, and manganese). Their zinc and copper capsules, in particular, display unique fluorescent properties. Furthermore, the researchers expect to be able to prepare multicolor fluorescence composites by the simple insertion of appropriate fluorescent molecules into the isolated cavity of the nanocapsules.
The M2L4 capsules self-assemble from two metal ions and four bent ligands that include anthracene fluorophores (fluorescent parts). X-ray crystallographic analysis verified the closed shell structures where the large interior cavities of the capsules, around one nanometer in diameter, are shielded by eight anthracene panels.
The zinc capsule emitted strong blue fluorescence with a high quantum yield (80%), in sharp contrast to the weakly emissive nickel and manganese capsules and the non-emissive palladium, platinum, and cobalt capsules. The fluorescence of the copper capsule, on the other hand, depends on the solvent; for example, it shows blue emission in dimethyl sulfoxide but no emission in acetonitrile. This study is the first to show such emissive properties of molecular capsules bearing an isolated large cavity.
1. Li Zhiou et al., Chemistry - A European Journal 18,8358 (2012).
SOURCE: Tokyo Institute of Technology; www.titech.ac.jp/english/file/20120712_PressRelease.pdf